Weight painting two unconnected meshes
Your screenshot is showing the weights relative to the shin bone only. Every vertex is affected by all weights assigned relative to all others bones (probably foot, in example): if you want all the vertices of the bottom ring of the leg to move exactly as the upper ring of the foot, all thoose vertices must be weighted in the exact same way relatively to all the bones in which you have some weight.

See this answer for more infos:

How can my animation animate if there is no vertex weights?